1. Department of Pediatrics, University of Tsukuba Hospital, Tsukuba, Ibaraki, Japan
2. Health and Environmental Risk Division, National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan
3. Department of Biostatistics, Faculty of Medicine, University of Tsukuba, Tsukuba, Ibaraki, Japan
4. Department of Neonatology, Ibaraki Children's Hospital, Mito, Ibaraki, Japan
5. Department of Obstetrics and Gynecology, Faculty of Medicine, University of Tsukuba, Tsukuba, Ibaraki, Japan
6. Department of Child Health, Faculty of Medicine, University of Tsukuba, Tsukuba, Ibaraki, Japan